The present invention relates to a manufacturing method for fabricating a semiconductor device, and particularly relates to a technique which is capable of being suitably used for a semiconductor device in which a non-volatile memory and a normal MISFET (Metal Insulator Semiconductor Field Effect Transistor) are combined.
Semiconductor integrated circuits (for example, LSI: Large Scale Integrated circuit) having a non-volatile memory combined with a logic circuit, a memory circuit, an analog circuit or the like, have been in widespread use. MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) including a silicon oxide (SiO2) film in a gate insulating film, among MOSFETs, are frequently used in the logic circuit or the like. On the other hand, FETs (Field Effect Transistors) including a charge storage film in the gate insulating film may be used in the non-volatile memory. The charge storage film has a trap level, and carriers are trapped (stored) in the trap level. Thereby, information is stored using a phenomenon in which the threshold voltage of the FET changes. The carriers trapped in the trap level are held even in a case that the supply of power to a circuit is stopped, and thus function as the non-volatile memory. As the charge storage film, a silicon nitride (Si3N4) film is frequently used, and is formed of a three-layer structure interposed in a potential barrier film between a gate electrode and a channel. As the potential barrier film, a silicon oxide (SiO2) film is frequently used, and the film of the three-layer structure is called an ONO (Oxide/Nitride/Oxide) film. Such an FET is called a MONOS (Metal/Oxide/Nitride/Oxide/Semiconductor) type FET from its structure. In a manufacturing method for an LSI circuit having the non-volatile memory, a gate insulating film of a normal FET and an ONO film are required to be formed on the same semiconductor substrate, and thus various techniques have been proposed.
In one example, JP-A-2012-216857 discloses a technique for forming a MOSFET and a MONOS type FET on the same semiconductor substrate. In first and second embodiments, a manufacturing method is disclosed in which an ONO film and a polysilicon film for forming a gate electrode of a MONOS type FET are first formed on the entire surface of the semiconductor substrate, a region having the MOSFET formed therein is opened, and then a gate oxide film and a polysilicon film of the MOSFET are formed. In third and fourth embodiments, a manufacturing method is disclosed in which the gate oxide film and the polysilicon film of the MOSFET are reversely first formed on the entire surface of the semiconductor substrate, and then the ONO film and the polysilicon film for forming the gate electrode of the MONOS type FET are formed.